The present invention relates to an electron emission source typically suitable for an ultrathin display, a production method thereof, and a display using the electron emission source.
Conventionally, there has been proposed an ultrathin display of a type in which a panel-like electron emission source is provided inside a fluorescent screen of the display and a number of microchips made from an electron emission material are formed in each of pixel regions of the electron emission source, wherein the fluorescent screen is made luminous by exciting the microchips in the corresponding pixel regions in response to specific electric signals.
The electron emission source of this type includes a plurality of strip-like cathode electrode lines (first electrodes); a plurality of strip-like gate electrode lines (second electrodes) formed on the cathode electrode lines in such a manner as to intersect the cathode electrode lines; and the microchips disposed in an intersection region (corresponding to one pixel of the display) located between each of the cathode electrode lines and each of the gate electrode lines.
The configuration of the prior art electron emission source will be more concretely described with reference to FIG. 1. A plurality of strip-like cathode electrode lines 103 are formed on a lower substrate 101 made from typically a glass material; an insulating layer 104 is formed on the cathode electrode lines 103 excluding connection ends 103a thereof; and a plurality of strip-like gate electrode lines 105 are disposed on the insulating layer 104 in such a manner as to intersect the cathode electrode lines 103. The connection ends 103a of the cathode electrode lines 103 and connection ends 105a of the gat e electrode lines 105 are connected to a control means 109.
A number of fine holes 17 are formed in an intersection region between each of the cathode electrode lines 103 and each of the gate electrode lines 105. The fine holes 17 pass through the gate electrode line 105 and the insulating layer 104 and reach the surface of the cathode electrode line 103. A microchip 106 is provided in each of the fine holes 17 in such a manner as to project from the bottom of the fine hole 17.
The microchips 106 are each formed into an approximately conical shape by using an electron emission material such as molybdenum, and are disposed on the cathode electrode lines 103. The height of the leading end of the conical body of each microchip 106 is substantially the same as the height of the film surface of the gate electrode line 105. In this way, a number of the microchips 106 are provided in the intersection region between each of the cathode electrode lines 103 and each of the gate electrode lines 105, and the intersection region forms a pixel region which corresponds to one pixel of the display.
The electron emission source, designated by reference numeral 100 in FIG. 1, is operated by selecting a desired one of the cathode electrode lines 103 and a desired one of the gate electrode lines 105 and applying a specific voltage therebetween by the control means 109, to apply the specific voltage to the microchips 106 in the corresponding pixel region, thereby allowing electrons to be emitted from the leading ends of the microchips 106 on the basis of the tunnel effect. In the case of using the microchips 106 made from molybdenum, the specific voltage applied to each microchip 106 is set at such a value as to obtain the strength of an electric field near the leading end of the conical body of the microchip 106 in a range of about 108 to about 1010 V/m.
When the electron emission source 100 shown in FIG. 1 is used for a display, a transparent upper substrate (not shown) is assembled to the electron emission source 100 in such a manner as to be disposed on the gate electrode lines 105 with a gap put therebetween. Strip-like anode electrode lines are formed on the under face of the upper substrate and phosphor stripes are formed on the anode electrode lines. The anode electrode lines are made from a transparent conductive material such as ITO (Indium Tin Oxide). Connection ends of the anode electrode lines are connected to the control means 109. A space between the upper substrate and the lower substrate 101 is configured as a high vacuum region.
Such a display is operated such that electrons emitted from the microchips 106 in a desired pixel region by exciting the pixel region are accelerated by a voltage applied between the corresponding cathode electrode line 103 and anode electrode line, passing through the vacuum region between the gate electrode lines 105 and the anode electrode lines, and reach the corresponding phosphor stripe. When the electrons are thus made incident on the phosphor stripe, visual light is emitted from an electron-incident portion of the phosphor stripe and is observed through the transparent anode electrode line and upper substrate.
The above-described prior art electron emission source has the following problems:
At first, it is difficult to uniformly produce the microchips 106, particularly, the leading ends thereof without occurrence of differences in size and/or shape therebetween. If there occur differences in size between the microchips 106, the amount of electrons emitted from the microchips 106, that is, the amount of a current flowing the microchips 106 differs for each pixel. As a result, luminous spots formed on the upper substrate of the display become non-uniform, thereby degrading the image quality.
At second, gas remaining in the high vacuum region between the lower substrate 101 and the upper substrate is ionized to sputter the microchips 106, so that the shapes of the leading ends of the microchips 106 tend to be easily deteriorated with an elapsed time, thereby reducing the amount of a current flowing in the microchips 106.
At third, since the flying direction of electrons emitted from the microchips 106 is extended by about xc2x130xc2x0 with respect to the direction perpendicular to the cathode plane, the luminous region of the phosphor screen composed of the phosphor stripes is enlarged. This is disadvantageous in terms of high-definition of the display.
At fourth, the prior art electron emission source has a problem in its production steps. The microchips 106 are generally formed by vapor-depositing a refractory metal such as molybdenum in vacuum with a lift-off spacer left on the gate electrode lines 105. To be more specific, the conical microchips 106 are formed in self-alignment by reversely making use of the poor step-coverage which is the characteristic of the vacuum vapor-deposition process, and then the refractory metal such as molybdenum deposited on the lift-off spacer is removed by a lift-off process. At this time, metal pieces peeled by lift-off enter in each fine hole, to cause short-circuit between the microchip 106 and the gate electrode line 105, thereby causing short-circuit between the cathode electrode line 103 and the gate electrode line 105. As a result, there arises a problem in degrading the production yield.
To solve the above-described problems, an electron emission source of a type using electron emission planes has been disclosed in Japanese Patent Laid-open No. Hei 8-55564. According to this prior art technique, since the electron emission planes are used in place of the microchips, it is possible to avoid the above-described problems associated with the microchips.
Such a technique, however, has another problem that since the distance between the cathode electrode lines 103 and the gate electrode lines 105 of a display according to this technique is longer than that in the case of using the microchips 106, a high voltage is required to be applied between the electrode lines 103 and 105 in order to ensure a sufficient amount of a current for obtaining a high brightness, thereby bringing a possibility of occurrence of electric breakdown.
A first object of the present invention is to provide an electron emission source which is capable of being driven at a low voltage, making a current amount uniform, reducing the extension of electron beams, prolonging the service life, and reducing the possibility of short-circuit between electrodes.
A second object of the present invention is to provide a method of producing the above electron emission source.
A third object of the present invention is to provide a display using the above electron emission source.
To achieve the above first object, according to the present invention, there is provided an electron emission source including: a first electrode extending on a substrate; a second electrode extending on the first electrode via an insulating layer; one or a plurality of fine holes opened in the second electrode in such a manner as to reach the first electrode through the insulating layer; a metal made projecting structure having a trapezoidal shape in cross-section, the projecting structure being formed in each of the one or plurality of fine holes in such a manner as to project from a portion, positioned in the fine hole, of the first electrode; and an electron emission portion made from an electron emission material, the electron emission portion being formed on the upper surface of the projecting structure; wherein a projecting body composed of an enormous number of fine projections is provided on the surface of the electron emission portion.
To achieve the above second object, according to the present invention, there is provided a method of producing an electron emission source including the steps of: forming a first electrode, an insulating layer, and a second electrode on a substrate in this order; forming one or a plurality of fine holes in the second electrode in such a manner that the one or plurality of fine holes reach the first electrode through the insulating layer; forming a metal made projecting structure having a trapezoidal shape in cross-section in each of the one or plurality of fine holes in such a manner that the projecting structure projects from a portion, positioned in the fine hole, of the first electrode; and forming, an electron emission portion made from an electron emission material on the surface of which a projecting body composed of an enormous number of projections are provided, on the upper surface of the projecting structure.
To achieve the above third object, according to the present invention, there is provided a display including: an electron emission source including: a first electrode extending on a substrate; a second electrode extending on the first electrode via an insulating layer; one or a plurality of fine holes opened in the second electrode in such a manner as to reach the first electrode through the insulating layer; a metal made projecting structure having a trapezoidal shape in cross-section, the projecting structure being formed in each of the one or plurality of fine holes in such a manner as to project from a portion, positioned in the fine hole, of the first electrode; and an electron emission portion made from an electron emission material, the electron emission portion being formed on the upper surface of the projecting structure; wherein a projecting body composed of an enormous number of fine projections is provided on the surface of the electron emission portion; and an anode electrode and a phosphor screen disposed opposite to the electron emission source with a gap put therebetween; whereby electrons are emitted from the electron emission portion by applying a voltage between the first and second electrodes, and are made incident on the phosphor screen to make luminous the phosphor screen.
The electron emission source of the present invention, which is configured such that the projecting structure projects from the first electrode and the electron emission portion is formed on the projecting structure, is advantageous in that as compared with the prior art electron emission source using the electron emission planes, it is possible to significantly shorten the distance between the electron emission portion and the second electrode, and hence to ensure a sufficient current amount even if a voltage applied between the first and second electrodes is lowered.
In the case of using carbon as the electron emission material, it is possible to ensure a current amount necessary for the display only by applying an electric field strength of about several tens V/xcexcm or less to the electron emission portion, that is, only by applying a voltage of several tens V or less between the first and second electrodes. That is to say, it is possible to drive the electron emission source at a low voltage.
Further, according to the electron emission source of the present invention, since the projecting body composed of an enormous number of projections is provided on the surface of the electron emission portion, electrons are easily emitted from the electron emission portion. As a result, it is possible to drive the electron emission source at a lower voltage.
Since the electron emission portion formed on the projecting structure having a trapezoidal shape in cross-section is not sharpened, that is, flattened unlike the microchip, it is easy to uniformly produce the electron emission portions, and thereby it is possible to solve the problem that the current amount varies for each pixel.
The flat shape of the electron emission portion brings another advantage that electrons emitted from the electron emission portion are allowed to be filed while being not extended so much.
The flat shape of the electron emission portion brings a further advantage that even if gas remaining in the vacuum region is ionized to sputter the electron emission portion, the shape of the electron emission portion is not changed, and accordingly, it is possible to eliminate the inconvenience that the current amount is reduced with an elapsed time and hence to prolong the service life.
Since the distance between the second electrode and the electron emission portion is longer than that in the case of using the microchips, it is possible to suppress occurrence of short-circuit between the electrodes and hence to improve the production yield.